A gamma camera is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. Applications of scintigraphy include early drug development and nuclear medical imaging to view and analyze images of the human body or the distribution of medically injected, inhaled, or ingested radionuclides emitting gamma rays.
A gamma camera consists of one or more flat crystal planes (or detectors) optically coupled to an array of photomultiplier tubes, the assembly is known as a “head”, mounted on a gantry. The gantry is connected to a data processing system that both controls the operation of the camera as well as acquisition and storage of acquired images.
The system accumulates events, or counts, of gamma photons that are absorbed by the crystal in the camera. Usually a large, e.g., 40 cm×50 cm, flat crystal of sodium iodide with thallium doping in a light-sealed housing is used.
The crystal scintillates in response to incident gamma radiation. When a gamma photon leaves the patient (who has been injected with a radioactive pharmaceutical), it knocks an electron loose from an iodine atom in the crystal, and a large number of light photons, is produced when the dislocated electron again finds a minimal energy state. The initial phenomenon of the excited electron is similar to the photoelectric effect and (particularly with gamma rays) the Compton effect. After the light photons are produced, they are detected, e.g., a detected event. Photomultiplier tubes (PMTs) behind the crystal detect the photons and a computer sums the counts. The computer reconstructs and displays a two dimensional image of the relative spatial count density on a monitor. This reconstructed image reflects the distribution and relative concentration of radioactive tracer elements present in the organs and tissues imaged.